For those who dug into history, the phenomenon of strange lights weren't confined solely to being witnessed in the sky. Many were seen in large bodies of water, too, often flying out of or into the air. Even the voyage of Columbus had the ship's crew take notice of them.
It was like a glint on the water's surface. Something glistening, surely reflecting the sunlight from up above. It could be seen from a distance, then, far too quickly for anything living, seemed to dart an an impossible speed to somewhere else. It was only when, catching sight of its irregular motions and speed, it neared closely enough to have to be emanating from beneath the waves. One might be fooled for assuming it had to be a submarine, but the glowing source of light was alternating between slow gliding motions and then zapping off at impossible angles, much too fast to be any man-made contraption. More like... Aquatic ball lightning.
Angler fish weren't meant to live in fresh water.
Or get nearly that big.
And when it showed interest in him, it shot over, just as fast. A sudden shimmer of activity, as fast as any lightning strike, coming to rest directly beneath him. Then to the boat, then back to him. Not even the slightest disturbance being felt in the water, itself. Just that eerie source of bright light.
And it started, slowly, to ascend through the lake's murky depths.